Apparatus to separate pieces of mail such as envelopes whose address information is readable by machine (printed destination address) from pieces of mail the address of which cannot be read by machine (handwritten destination address) is known from such patents as U.S. Pat. No. 3,432,032 issued Mar. 11, 1969, to D. G. Curphey et al. In that disclosure called "Presorting", each envelope passes a scan device having 72 photosensitive elements in vertical alignment. The elements take continuous readings during the entire transverse period of the envelope to produce 2 sets of 32 parallel output signals for transmission to decision circuits.
In the apparatus shown by this reference, photosensors are strategically located to signal the entry of an envelope into the area monitored by the photosensitive elements. The photosensor activates the elements to continue the production of output signals until a trailing edge sensor indicates that the envelope has passed the scan area.
In the reference machine, detection of skewing of the address is accomplished within the logic network by checking the difference between readings in a first and second interrogation cycle and by combining skew detection with a determination of character height. Characters above a predetermined height are considered non-machine readable leading to a decision of that type.
Further, the reference machine uses an optic fiber bundle to illuminate an area of the envelope corresponding to the length of the photosensitive array which is disposed in close physical proximity to the envelope. A number of problems arise in such a device such as damage of the fibers and the photosensitive array because of the closeness to the moving mail and the necessity for custom fabrication of each scan unit. Further, the requirements for the parallel processing of 32 parallel signals seriously limits the amount of processing implemented in each channel because of cost considerations. This drawback is amplified if the area of the envelope to be scanned is increased in dimension.